1. Field of the invention
The invention relates to the field of photography. More particularly, the invention relates to the field of still photography. More particularly yet, the invention relates to the removal of the background from a photograph consisting of an object of interest set against a background so as to produce an image of the object by itself.
2. Description of the Prior Art
In the field of commercial photography, the isolating of an object of interest from the background photographed with that object is referred to as “silhouetting” the image. Such silhouetted images are often desired in commercial photography used for advertising and catalog purposes. Examples of silhouetted images can be seen in most catalogs of merchandise, where the products offered are shown as simply placed on the catalog page, without any background at all (apart from the color of the page). In order to present a clean and natural image, it is, of course, critical that the original background not contaminate the image and that it be stripped very precisely and cleanly from the image.
Regardless of the level of resolution with which the image is photographed, it is desirable to be able to cut away the background and show just the object of interest, for later transfer to catalog pages and the like. For high-resolution digital color photography of still objects, the image is generally created by three separate shots though in the case of the technology patented by the present inventor two shots may be sufficient.
One way to strip off the background from a digitized image is by “brute force,” namely the manual removal of the background using techniques such as are available in off-the-shelf programs such as Photoshop®. This, however, can be extremely tedious, especially near the interface between the background and the object of interest. Thus, techniques have been developed over the years so as to automate the process.
The most common automated method for background stripping has involved “chroma replacement,” In preparation for using this method to generate a silhouetted image, the object of interest is photographed in front of a background that is all the same color, ideally a color different from those of the object of interest. Most commonly, the color has been blue, and occasionally green, background. After the photography is completed, standard computer techniques are used to eliminate from the composite photograph all portions (pixels) that have the background color. More particularly, the stripping program is directed to remove from the photograph all pixels having a color that lies within a pre-programmed bandwidth centered on the background color. This chroma replacement has, inherently, several disadvantages, especially when used with high quality, high resolution studio photography of still objects. An obvious disadvantage is that it will remove from the object of interest all portions that have a color falling within that defined bandwidth. This means that a subsequent processing must be used wherein those parts are added back into the photograph. Another problem arises because the color of the background—which, by its nature, is in close proximity to the object—is reflected onto the object, thereby creating a transition area that makes it difficult to accurately distinguish between background and object during the stripping process. This can result in border portions of the object being stripped away. If the surface of the object with the reflected color is sufficiently different from the color of the pure background, that region will not get stripped away, but can end up looking strangely colored once the background is gone.
Many attempts have been made to improve the chroma replacement process so as to eliminate the above-mentioned drawbacks and to create clean silhouetted images with a minimum of processing effort. Such an attempt in connection with single-shot photography of moving objects is disclosed in U.S. Pat. No. 5,948,500 (Oles; issued 1999), which also explains why the chroma replacement technique has not been widely used in the commercial photography industry in connection with high quality studio shots. Nevertheless, the solution of Oles stays within the context of the chroma-replacement technique, and thus did not address the problems inherent in that technique. Furthermore, Oles is not directed at high resolution still photography. U.S. Pat. No. 8,134,348 (Berman et al.; issued 2000) addresses the particular problem in chroma replacement presented by objects that have semi-transparent edges (such as a person with waving hair). The method of Berman et al. creates a number of frames of the background, with and without an image of the object, determines a transition area in which some transparency exists at the boundary of the object and the background, and strips the background from around the photographed object. Oles and Berman et al. both have the drawbacks mentioned above, in that the colors on the person or object being photographed must be coordinated so as not to coincide with the bandwidth of the background color.
Color contamination from the background itself creates problems. Most frequently, a saturated color is used as the background because it is easier to strip the background from the image later if it can be defined within a narrow bandwidth of color. Such colors, however, can spill onto the object and color-contaminate an image to an extent that is unacceptable for commercial photography. On the other hand, a white or light-colored background makes the bottom of an image look lighter and creates a perceptibly strange impression once the background is gone. Backgrounds of medium gray may reduce color contamination, but computerized processes cannot clearly differentiate between the background gray and the outline of the image.
Today, in commercial photography establishments using digital photography techniques, a person manually traces around the silhouette of the image on a computer screen in order to provide the computer with an outline from which to remove the background. This is an extremely tedious and time-consuming task.
What is therefore needed is an apparatus and a method of removing the background from a digitally photographed image, cleanly and precisely, with fewer processing operations than are now required. What is further needed is such an apparatus and a method that functions independently of color. What is yet further needed, in view of the expense of high-quality photography equipment, is such an apparatus that is adaptable to existing camera equipment and lenses.